Project Year 2015

Omega-3 requirement for salmon

150 grams of farmed salmon a week is sufficient to meet the needs for omega-3 fatty acids in humans. But what is sufficient for the salmon?

Salmon require the long marine omega-3-fatty acids EPA and DHA in the diet to maintain good health. These fatty acids are known to have a role in developing eye and brain function and for good growth, and they are probably also essential for the immune system.

Nofima’s research has previously shown that salmon have a natural but limited ability to transform a short omega-3 fatty acid from plants to marine omega-3. This ability is greatest when the level of marine omega-3 in feed is low. Research has also shown that the ability varies between fish with different genetic backgrounds.

So how little marine omega-3 can farmed fish get by on? Nofima is approaching an answer by studying fat metabolism throughout the salmon’s life, where they have given salmon from 0 to 2 per cent EPA and DHA in the feed, from initial feeding to slaughter at 4 kilos. They have analyzed the fish regularly, and found which level of EPA and DHA in the feed that results in the maximum own production of marine omega-3 in salmon.

In terms of the most efficient utilisation of resources, it pays to have one per cent or less of marine omega-3 in the feed, as the salmon’s own production peaks.

However, one per cent is too low for the fish to maintain good health in a demanding environment, says Bente Ruyter, senior researcher with Nofima. In trials in the sea she has seen that salmon on a omega-3 diet deficient showed higher mortalities than salmon on a high omega-3 diet. This salmon was treated for sea lice repeatedly and the sea temperature was high.

“In order to secure a robust salmon in the sea that can withstand the handling and environmental stressors it faces in practice, farmed salmon seem to need more than 1 per cent marine omega-3 in the diet to maintain good health. However, if one succeeds with closed technology and control of environmental factors, the salmon can probably cope with less omega-3 in the diet. At the same time, it’s possible to exploit the genetic potential the fish have in transforming plant fat to marine fat,” Ruyter says.

The content in current feed varies, but all are well above 1 per cent.